I'll add that pressure, in and of itself, was never the problem with the Garand, which has an extremely strong action. The problem was the gas impulse at the gas port which is the pressure at the gas port times the amount of time it takes the bullet to pass from the gas port to the muzzle. That's what determines how much gas may be pushed in through the gas port. In the Garand, which has its gas port just 1.5 inches from the muzzle, this impulse changes a lot with powder burn rate, so where it is perfectly OK to reach commercial peak pressure with a powder fast enough not to create too much muzzle pressure, it is not OK to reach that same peak pressure with a slower powder because the muzzle pressure would then be too high and can pressurize the gas cylinder to the point it can bend the Garand operating rod.
The M1A and M14, on the other hand, have the gas port roughly 8 inches back from the muzzle. At that shorter distance from where the bullet is at the pressure peak (about one to two inches into the barrel) the difference in pressure produced by different burn rate powders loaded to the same peak pressure is less. Add to this that the gas piston in the M1A/M14 closes off the gas port when it starts to move (the regulated gas system) and that the gas piston and op-rod are much shorter and stronger than the Garand op-rod, and you find the load tolerance is vastly wider in the M1A/M14 rifle family than it is in the Garand.